The invention relates to a device for examining a test object by means of gamma or X-rays, comprising a primary X-ray source for generating at least one primary X-ray pencil beam which is directed onto the test object, and also comprising at least one slit diaphragm which is arranged between the test object and a detector and which directs secondary X-rays (Compton effect) produced by the primary X-rays in the test object onto at least one detector.
Devices of this kind are known from EP-A 184 247 which corresponds to U.S. Pat. No. 4,750,196 and are used for the non-destructive testing of high-quality components, for example components used in the aerospace industry.
The intensity of the pencil-shaped primary X-ray beam penetrating the material of the test object is changed due to absorption and scattering. As the primary radiation energy is higher, the Compton scattering becomes dominant, which scattering propagates substantially spherically from each point of the material on the path of the primary radiation. The intensity of the Compton scattering, therefore, is substantially equal in all angular directions. Notably materials such as light metal, plastics, laminates or ceramics can notably be advantageously tested.
Particularly simple test devices are obtained when the components of the secondary radiation which are backscattered relative to the primary radiation direction are detected by suitable detectors. The detectors are then arranged on the same side of the test object as the primary X-ray source.
The slit diaphragm operates in the same way as a pinhole camera. Its position in space relative to the detector determines from which of the points of the test object, situated on the primary beam path, scattered radiation reaches the detector. A three-dimensional zone of the test object can be examined by displacement of the test object relative to the examination device or vice versa.
Points of the test object which succeed one another in the direction of the primary X-ray beam in a given depth range can be scanned without displacement of the test object or the examination device if use is made of array of several detectors. Furthermore, the primary X-ray beam can be shifted perpendicularly to the beam direction by means of a suitable deflection device, for example as described in EP-A 184 247, so that surfaces of the test object can be scanned without intricate displacement of the examination device.
For a predetermined spatial relationship between the test object and the examination device, the depth range that can be measured is predetermined by the geometrical relationship between the position of the slit diaphragm and the detectors.